Iti Gupta

Synthesis of 21-thia and 21-oxaporphyrin building blocks and boron–dipyrrin appended systems

Abstract A series of 21-thia and 21-oxaporphyrin building blocks bearing iodo-, ethynyl-and aldehyde functional groups were synthesized and characterized. These porphyrins are ideal building blocks for the construction of unsymmetrical porphyrin arrays containing two dissimilar porphyrin cores. The building blocks were used to construct boron–dipyrrin appended core-modified porphyrin systems under mild palladium coupling conditions. A preliminary steady state fluorescence measurements suggested that boron–dipyrrin unit transfers the energy to both 21-oxaporphyrin and 21-thiaporphyrin and the efficiency depends on the orientation of the boron–dipyrrin units and the core structure of the porphyrin.

Fluorescence properties of meso-tetrafurylporphyrins

Fluorescence properties of meso-tetrafurylporphyrins with N4, N3S and N2S2 porphyrin cores are studied by both steady-state and time-resolved fluorescence techniques and compared with the corresponding meso-tetraarylporphyrins. The study shows that the replacement of six-membered aryl groups with five-membered furyl groups at meso-positions alter the fluorescence properties considerably, as reflected in the large red shifts and broadening of fluorescence bands with reduction in quantum yields and singlet excited-state lifetimes. However, zinc(II) derivatives of meso-tetrafurylporphyrin and mesotetraarylporphyrin did not show significant differences in their emission properties.

Carbazole-corrole and carbazole-prophyrin dyads: synthesis, fluorescence and electrochemical studies†

Donor–acceptor type carbazole–corrole and carbazole–porphyrin dyads 4–9 were synthesized and characterized. Corrole and porphyrin containing one meso-p-iodophenyl group were coupled to N-butyl-3-ethynyl-carbazole by a modified Sonogashira reaction. All the dyads were characterized by HRMS mass, NMR, UV-vis absorption, fluorescence and electrochemical techniques. Fluorescence studies of dyads 4, 7 and 8 indicated energy transfer from the donor carbazole moiety to the corresponding acceptor corrole/porphyrin moiety (up to 80%). The electron-releasing N-butyl-carbazole group affects the electronic properties of the corrole and porphyrin macrocycles in the dyads 4–9. Electrochemical studies revealed that dyads 4 and 5 are difficult to reduce compared to their corresponding monomers, as reflected by the cathodic shift in their reduction potentials. Meanwhile, dyads 6–9 exhibited an anodic shift in their reduction potentials, suggesting that they are easy to reduce compared to their corresponding monomers.

Synthesis of meso-furyl porphyrins with N4, N3S, N2S2 and N3O porphyrin cores

Abstract A series of meso-furyl porphyrins with four different porphyrin cores (N4, N3S, N2S2 and N3O) were synthesized and characterized. The comparison of NMR, optical and fluorescence properties of meso-furyl porphyrins with porphyrins with six-membered aryl groups indicates that electronic properties of porphyrins were changed drastically on the introduction of furyl groups at meso positions. The maximum shifts in spectral bands were observed for meso-furyl porphyrins with N2S2 core. On protonation, the absorption bands of meso-furyl porphyrins were further red shifted. All these changes were ascribed to the possibility of more planarity of the meso-furyl porphyrins due to the small size of the furyl groups which results in extending the π-delocalisation of the porphyrin ring in to the furyl groups.

Synthesis of functionalized thia analogues of phlorins and covalently linked phlorin–porphyrin dyads

The 21,23-dithia and 21-thia analogues of phlorins and mono-functionalized thiaphlorins were synthesized using easily available precursors and the mono-functionalized thiaphlorins were used further to synthesize the first examples of three covalently linked thiaphlorin-porphyrin dyads.

Synthesis of 21-oxoporphyrin building blocks and energy donor appended systems

Abstract A series of 21-oxoporphyrin building blocks bearing iodo- and ethynyl functional groups were synthesized and characterized. A boron–dipyrrin unit appended 21-oxoporphyrin was constructed using the building blocks under mild palladium coupling conditions which exhibited efficient energy transfer from boron–dipyrrin to 21-oxoporphyrin.

Synthesis of meso-furyl porphyrins

Abstract Three meso -furyl porphyrins with N 4 , N 3 S and N 2 S 2 porphyrin cores were synthesized and characterized. The absorption bands of meso -furyl porphyrins experienced large red shifts compared to meso -aryl porphyrins and the maximum red shifts were observed for the meso -furyl porphyrin with the N 2 S 2 core.

Synthesis, Structure, and Optical Studies of Donor–Acceptor‐Type Near‐Infrared (NIR) Aza–Boron‐Dipyrromethene (BODIPY) Dyes

Six donor-acceptor-type near-infrared (NIR) aza-boron-dipyrromethene (BODIPY) dyes and their corresponding aza-dipyrrins were designed and synthesized. The donor moieties at the 1,7-positions of the aza-BODIPY core were varied from naphthyl to N-phenylcarbazole to N-butylcarbazole. The 3,5-positions were also substituted with phenyl or thienyl groups in the aza-BODIPYs. Photophysical, electrochemical, and computational studies were carried out. The absorption and emission spectra of aza-BODIPYs were significantly redshifted (≈100 nm) relative to the parent tetraphenylaza-BODIPY. Fluorescence studies suggested effective energy transfer (up to 93 %) from donor groups to the aza-BODIPY core in all of the compounds under study. Time-dependent (TD)-DFT studies indicated effective electronic interactions between energy donor groups and aza-dipyrrin unit in all the aza-BODIPYs studied. The HOMO-LUMO gap (ΔE) calculated from cyclic voltammetry data was found to be lower for six aza-BODIPYs relative to their corresponding aza-dipyrrins.

Donor–acceptor type A2B2 porphyrins: synthesis, energy transfer, computational and electrochemical studies

A series of donor–acceptor type trans-A2B2 porphyrins and their Zn(II) and Pd(II) complexes 5–13 have been synthesized and characterized by various spectroscopic techniques. The effect of the donor moieties (e.g., N-butylcarbazole, N-butylphenothiazine, and triphenylamine) on the spectroscopic properties of the porphyrins has been studied. The structural changes indeed affected the optical and electrochemical properties of these porphyrins. Higher energy shifts of the Soret bands were observed for porphyrins upon varying the donor moieties. The electrochemical studies of all the derivatives indicated increased interactions between the donor groups and the porphyrin core, which in turn are reflected in the anodic shifts in their reduction potentials. Both steady-state and time-resolved fluorescence studies revealed effective energy transfer (EET; up to 87%) from donor groups to the porphyrin core in the porphyrins, 5–10. The palladium(II) porphyrin complexes, 11–13, showed characteristic phosphorescence in the near IR region. Density functional theory (DFT) studies support the presence of donor–acceptor interaction between the porphyrin core and the meso-substituents in the dyads. Density functional theory (DFT) and time dependent-density functional theory (TD-DFT) studies showed that in 5, 8 and 11, the transitions are of π → π* type; whereas in the other molecules viz.6, 7, 9, 10, 12 and 13 intramolecular charge transfer (ICT) is involved in all the respective highest intensity absorption transitions.

Donor acceptor type ferrocene substituted aza-BODIPYs: Synthesis, optical and electrochemical studies

Two ferrocene substituted aza-BODIPYs and their corresponding aza-dipyrrins were synthesized and studied. All the compounds were characterized by HRMS, NMR, IR, absorption spectroscopy and cyclic voltammetry techniques. Absorption spectra indicated intramolecular electron transfer from the ferrocene to the aza-BODIPY core. The X-ray crystal structure of 1,7-bisferrocenyl-aza-BODIPY suggested moderate interactions between the ferrocene moieties and aza-BODIPYs core. Ferrocenyl-aza-BODIPYs were non-emissive due to electron transfer from ferrocene moieties to boron aza-dipyrrin core. However the emission of these compounds was dramatically enhanced by oxidizing the ferrocene moieties to ferrocenium ions, which prevents electron transfer between these moieties. Cyclic voltammetry studies suggested that aza-BODIPYs were easier to be reduced as compared to their corresponding aza-dipyrrins.